How are red-green color blindness and hemophilia examples of sex-linked inheritance?

Sourav PanNovember 8, 2024

Answered

Red-green color blindness and hemophilia are both classic examples of sex-linked inheritance, specifically linked to the X chromosome. Here’s how each condition exemplifies this inheritance pattern:

Red-Green Color Blindness

1. Genetic Basis:
   • Red-green color blindness is primarily caused by mutations in genes located on the X chromosome that are responsible for producing photopigments in the cone cells of the retina. The genes involved are crucial for normal color vision, and mutations can lead to deficiencies in perceiving red and green colors.
2. Inheritance Pattern:
   • X-Linked Recessive Inheritance: The gene for red-green color blindness is recessive. Males (XY) have only one X chromosome, so if they inherit an X chromosome with the color blindness allele (let’s denote it as XcXc), they will express the condition because there is no corresponding allele on the Y chromosome to mask it. For example, a male with genotype XcYXcY will be color blind.
   • Females (XX), on the other hand, must inherit two copies of the recessive allele (one from each parent) to express color blindness. A female with genotype XcXcXcXc will be color blind, while a female with genotype XcXXcX will be a carrier but not express the condition.
3. Transmission:
   • A color-blind father cannot pass the color blindness allele to his sons (since he passes his Y chromosome), but he will pass it to all his daughters, making them carriers if they inherit a normal allele from their mother. Thus, red-green color blindness is more common in males than females due to this inheritance pattern.

Hemophilia

1. Genetic Basis:
   • Hemophilia, particularly Hemophilia A and B, is caused by mutations in genes located on the X chromosome that are essential for blood clotting factors (Factor VIII for Hemophilia A and Factor IX for Hemophilia B). These mutations lead to a deficiency in clotting factors, resulting in prolonged bleeding episodes.
2. Inheritance Pattern:
   • X-Linked Recessive Inheritance: Similar to red-green color blindness, hemophilia follows an X-linked recessive pattern. Males with one affected X chromosome (genotype XhYXhY) will express hemophilia because they lack a second X chromosome that could carry a normal allele. Females must have two affected alleles (genotype XhXhXhXh) to exhibit symptoms of hemophilia; otherwise, they may be carriers (genotype XhXXhX) without showing symptoms.
3. Transmission:
   • An affected male can only pass his Y chromosome to his sons, meaning he cannot transmit hemophilia to them. However, he will pass his affected X chromosome to all his daughters, making them carriers. If a carrier female has children with a healthy male, there is a 50% chance for each son to inherit hemophilia and a 50% chance for each daughter to be a carrier